1. Field of the Invention
The present invention relates to a display device, and in particular to a column electrode driving circuit used for a display device that can perform multi-gray-scale displaying or multicolored displaying.
2. Description of the Related Art
In a liquid crystal display device, for example, many pixels (pixel areas) are provided over an entire display area in a matrix or in an array equivalent thereto, and row and column electrodes are provided for applying parts of a liquid crystal medium corresponding to these pixels with the respective electric fields according to the pixel information. The row electrodes are electrically conductive patterns that extend in a horizontal direction in the display area and the column electrodes are electrically conductive patterns that extend in a vertical direction in the same area.
Most active matrix type liquid crystal display devices are provided with, for example, TFTs (thin film transistors) as active elements to individually drive parts of the liquid crystal medium for each pixel, wherein the row electrodes are connected to the gates of the TFTs and the column electrodes are connected to the sources of the TFTs. Usually, one of the row electrodes corresponding to so-called scanning lines is selected for each horizontal scanning period of an image signal, and a gate voltage is supplied to the selected row electrode for simultaneously activating a group of TFTs connected to the selected row electrode. On the other hand, source voltages (pixel information signals) according to an image of the line are supplied to the activated TFTs to display the image of the line. Driving circuits for performing voltage-application to the row and column electrodes are provided, respectively.
There is one typical type of column electrode driving circuit which generates a number of gray-scale voltages necessary for different gray-scale levels required for the display device, and selects any of the gray-scale voltages in accordance with the pixel information for each pixel information signal so as to supply the selected gray-scale voltage to the corresponding column electrode. This driving circuit is arranged in such a manner that all gray-scale voltages are outputted via amplifiers. There is also a type of column electrode driving circuit that has amplifiers whose outputs are connected to the column electrodes, respectively.
The present inventor has noticed that the former would cause the amplifiers and their peripheral circuits to have an enormous power consumption. The present inventor has also conceived that the latter would have a feature of constantly operating quite a large number of amplifiers corresponding in number to dots for one line of the displayed image and again having an enormous power consumption, whereby it can be estimated that power consumption will increase further considering an increase in the number of dots based on a tendency to increase resolution in the future.
With the advent of portable devices or wearable devices such as cellular phones whose display functions have been unprecedentedly enhanced, there is a perception that notably the latest electronics devices are required not only to allow a long time operation with a limited battery capacity but also to have high-level display performance.